Mechanical steering gear internal friction: effects on the drive feel and development of an analytic experimental model for its prediction

The automotive steering system inevitably presents internal friction that affects its response. This is why internal friction phenomena are carefully monitored either by OEMs and by vehicle manufacturers. An algorithm to predict the mechanical efficiency and the internal friction of a steering gear system has been developed by the ZF-TRW Technical Centre of Gardone Val Trompia and the University of Brescia, Italy. It is focused on mechanical steering gear of the rack and pinion type. The main contributions to the overall friction have been identified and modelled. The work is based on theoretical calculation as well as on experimental measurements carried out on a purpose-built test rig. The model takes into account the materials used and the gear mesh characteristics and enables the prediction of the steering gear friction performance before the very first prototypes are built.